1. Field of the Invention
The invention pertains to the field of electronically controlled phase shifters and more particularly to accurately setting such phase shifters to commanded values.
2. Description of the Prior Art
Applications exist for electronically steerable antennas that require extremely low sidelobes, as for example, -50 dB with respect to the main beam peak. To realize such low sidelobe levels, phase errors across the aperture for each scan beam must not exceed 0.5.degree. RMS. Manufacture of an electronically scannable antenna to such type tight tolerances, even if feasible, would be extremely expensive. Calibration techniques, such as that disclosed by Herper et al in U.S. Pat. No. 4,270,129, issued in May 1981 and assigned to the assignee of the present invention, do not account for component variations due to aging and environmental conditions, requiring a repetition of the calibration procedure periodically, or as the environmental conditions dictate, in order to maintain the desired sidelobe levels. What is required is an automatic phase correction system capable of maintaining the required phase distribution for each scan angle of the antenna within the required tolerance limits to achieve the desired sidelobe levels.